Nonsingular Fixed-Time Fractional Order Sliding Mode Control of a Quadrotor Unmanned Aerial Vehicle Based on Disturbance Observer

This paper presents a nonsingular fixed-time fractional order sliding mode control (NFTFOSMC) for trajectory tracking of quadrotor unmanned aerial vehicle (QUAV) to enhance tracking performance. Firstly, a novel NFTFOSMC is proposed to guarantee the position and attitude system states of QUAV along the sliding surface within a fixed time upper bound and to mitigate the chattering phenomenon. Secondly, without relying on initial observation errors, a fixed-time disturbance observer (FTDO) is proposed to resistance to external disturbances during flight. Then, to address the issues of slow convergence speed and complex parameters in traditional double power reaching laws, an improved fast-varying power reaching law is designed, significantly shortening the reaching time. Finally, the proposed control strategy is verified by theoretical proof and simulation. Simulation results show that the proposed controller significantly reduces the trajectory tracking time of the QUAV in the presence of external disturbances and random white noise, reduces sliding mode chattering, improves tracking performance, and ensures that the upper bound of the convergence time is not affected by the system's initial state.